[Users] How to hide sender IP address and host name?

[Removed GDPR]

> It's the server that adds that header. Nothing the client can do
> about it.

Thanks for clarifying.

Is there any requirement (e.g. by some technological standard) that the
original sender's IP address must be in the headers or that is simply a
configuration up to the sysadmin who does configures the SMTP server?

And along these lines: are you aware of any mail service providers
which don't reveal the sender's IP address?